It is known that hyperlipidemia is a disease showing symptom of too high blood level of cholesterol and includes clinically some fundamental diseases such as chololithiasis, acute pancreatitis, xanthoma, etc. According to the recent epidemiological research, the hyperlipidemia has close relation with the appearance of arteriosclerosis, particularly atherosclerosis, and development thereof, and hence, this disease is one of the most important danger signal of ischemis heart diseases (e.g. angina pectoris, myocardial infarction) and cerebral infarction. From these viewpoints, it has been desired to find an excellent drug for the treatment of hyperlipidemia. The hypolipidemic drug is usually administered for a long period of time, and hence, the drug should be able to be administered easily (in smaller dose and in less administration time) and should exhibit the desired effect without undesirable side effect.
As a hypolipidemic drug, there have been clinically used or proposed various lipid metabolism improving drugs and cholesterol lowering drugs, such as clofibrate (chemical name: ethyl p-chlorophenoxyisobutyrate), nicotinic acid derivatives, anabolic steroids, phytosterols, anion exchange resins, and the like. However, these drugs are not necessarily satisfactory. For instance, although clofibrate has clinically widely been used, it shows less cholesterol lowering activity and has a problem of side effect, particularly hepatic toxicity (cf. J. K. Reddy et al., Nature, Vol. 283, 397-398, 1980). There has also been developed probucol of the formula: ##STR3## wherein t-Bu means tert-butyl, but this drug is still unsatisfactory.